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Flummoxed: my xPAP doesn't keep daylight savings time
#31
RE: Flummoxed: my xPAP doesn't keep daylight savings time
(11-16-2017, 12:42 PM)SnoringInOregon Wrote: The real annoyance is that the file timestamps the DreamStation writes to the SD card appear to already be in the Unix-standard UTC. So changing the time displayed by the DreamStation shouldn't matter. And yet it does.

Maybe changing the time only matters if I go back across noon? Someone already mentioned a problem like that for Resmed machines. Maybe the Respironics machines have a similar limitation? I remember distinctly that the DreamStation said 12:30 and I changed it back to 11:30, so I definitely crossed the boundary.
It could be a windows issue.

One of my secondary job functions is to provide traffic camera video to insurance companies, attorneys, and private individuals to file public records requests.

This morning, I got a call from an attorney in the east who claimed that I gave him video of the incorrect time.
I confirmed that it was correct, and the accident was visible on the CD.
He insisted that I had provided video from 1:00pm, and he had requested 11:00am.   I went back and pulled the original, and it was indeed correct.  Video from 1:10 was not available and physically could not have been provided.

On a hunch, I reset my computer to Central time.  Boom.   Not only did the video play back with 13:00 showing on the time stamp, BUT every file on my hard drive showed a save date/time 2 hours later.    Went back to Pacific time, and all times (and the video) were again correct.
I took a screenshot of the moment before the accident and emailed it to him, indicating the minute and second to look for and explaining that it was a Windows issue.
-- Rich
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#32
RE: Flummoxed: my xPAP doesn't keep daylight savings time
(11-16-2017, 10:33 PM)CB91710 Wrote: It could be a windows issue.

I'm talking about the DreamStation itself, not any operating system under which SleepyHead is running and interpreting files created by the DreamStation. I don't think the DreamStation runs Windows. It's probably running either Linux or some sort of real-time operating system. I myself run SleepyHead under macOS, not Windows, to read and interpret my data.

But I think you're right about the problem being very similar to time problems on WIndows.

The FAT32 filesystem format (invented for Windows) on the SD card doesn't inherently have a notion of timezones. There is only the "local time" at which a file was created.

I haven't checked into CD filesystem formats but I'd bet they have the same time limitations as SD cards. So I'm not surprised if you saw the file timestamps change when a CD was mailed across timezones. I'd be surprised if you didn't encounter those types of problems. Smile

Having said that, the DreamStation operating system puts UTC timestamps on the SD card files it creates. It doesn't bother using local timestamps. (To be strictly conforming to SD card time specs, the DreamStation should mark files with local time).

So, for example, if I turn off my DreamStation at 10 AM, the last file written to the SD card has a modification time of 6 PM. An 8 hour difference between Oregon and Grenwich, England. Obviously, SleepyHead knows about this and converts the SD card file timestamps from UTC to local time.

Keeping all of this straight was obviously too much for the DreamStation programmers. C'est la vie.
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